Doubly fed induction generator (DFIG) has a different fault characteristic when compared to traditional synchronous generator, and it has negative impacts on relay protection setting and cooperation, thus revealing the fault mechanism of DFIG from the point of analysis is an important issue. Based on vector model of DFIG, superposing the steady state and fault state, combined with the dynamic response circuit theory, and considering the different crowbar protection insertion time, a model for calculating the three-phase short-circuit current of DFIG is established. The analytical model takes into account the influence of the stator and rotor resistance, theoretically proving the origin of the decay time constant and corresponding relationship with the frequency component. The simulation results validate the model. Finally the paper quantitatively assesses the impacts of the degree of voltage dips, short-circuit occurred time and operation condition of DFIG on the short-circuit current.